Modern mobile communications are tending to provide high speed transmission of multimedia services for users. FIG. 1 is a schematic diagram illustrating a structure of a long term evolution (LTE) system.
In the system, user equipment (UE) 101 is a terminal device which receives data. Evolved universal terrestrial radio access network (E-UTRAN) 102 is a wireless access network using evolved Node B (eNodeBs, eNBs) or Node Bs (NodeBs, NBs) to provide the UEs 101 with interfaces for accessing the wireless network 102. Mobility management entity (MME) 103 manages mobility context, session context and security information of UEs 101. Serving gateway (SGW) 104 provides user plane functions. MME 103 and SGW 104 may reside in the same physical entity. Packet data network (PDN) gateway (PGW) 105 implements functions including accounting, lawful interception and so on, and may reside in the same physical entity with SGW 104. Policy and charging rules functions (PCRF) 106 provides Quality of Service (QoS) policies and charging rules. Serving GPRS support node (SGSN) 108 is a network node device providing routing for data transmission in the universal mobile telecommunications system (UMTS). Home subscriber server (HSS) 109 is a home sub system of the UE, and maintains user information including a current location of the UE, the address of the serving node, user security information, packet data context of the UE, and so on.
Group call services aim at providing a fast and effective mechanism to distribute data copies to users in a group. The concept of group call has been adopted in land mobile radio (LMR) systems for public security organizations. A typical application of group call is providing a “Push to Talk” (PTT) function. When group call is introduced into LTE systems, the LTE group call services need to support at least PTT audio communication and generate performances comparable to performances of conventional group communications. Group call services in system architecture evolution (SAE) are required to support UE in different states and UEs in different environments. LTE provides wide band data transmission, and group call services of LTE are required to support data communications of voice, video and the like.
Group communication service enabler (GCSE) of LTE enables group call by introducing functions of the application layer into 3rd generation partnership project (3GPP) standards. LTE users are divided into different groups, and a user may belong to one or multiple different GCSE groups. A user that receives GCSE service data in a GCSE group is referred to as a receiving group member, and a user that sends service data is referred to as a sending group member. Group call is communication between a sending group member and a receiving group member. Group call is also required to enable a user to communicate with multiple groups. For example, a user may carry out voice service with a group, and meanwhile perform video or data communication with another group.
In order to use air interface resources effectively, service data that is to be received by multiple receiving users is provided to the users via broadcasting and multicasting. The service is also referred to as multimedia broadcast and multicast service (MBMS). Each MBMS bearer provides services within its service area. Each cell in a service area has a dedicated control channel (MCCH) for transmitting MBMS signaling. Broadcast multicast service center (BM-SC) is an MBMS providing center which sends MBMS data to an MBMS gateway (MBMS-GW). MBMS-GW is a logic node or a network node between a BM-SC and an eNB, and is for sending/broadcasting MBMS data packets to each eNB that is to transmit data. The MBMS-GW sends a data packet to an eNB which transmits data to a user. Control signaling is sent by the BM-SC to the MBMS-GW, and then sent to E-UTRAN by an MME. Multi-cell/multicast coordination entity (MCE) is a node in E-UTRAN which receives MBMS signaling, decides the multicast-broadcast single-frequency network (MBSFN) transmission mode that is to be adopted and sends signaling to a corresponding eNB. In conventional mechanisms, a continuous area is defined, and eNBs in the area synchronously transmit the same MBMS signals on the same carrier to improve reception quality of MBMS services at users. The continuous area is referred to as a single frequency network (SFN) area. An SFN area includes a group of cells that cover a continuous geological area. The cells synchronously transmit a certain MBMS service using the same radio resources.
A GCSE service may be transmitted on a LTE evolved multimedia broadcast multicast service (eMBMS) bearer or on a unicast bearer. FIG. 2 is a schematic diagram illustrating an architecture of transmitting a GCSE service via an eMBMS bearer and via a unicast bearer. A GCSE application server (GCSE AS) sends service data to an MBMS GW, and the MBMS-GW sends the service data to multiple UEs via an eMBMS bearer. Alternatively, the service data may be sent to a PGW, and the PGW sends the service data to a UE via a unicast bearer.
But conventional eMBMS techniques cannot satisfy requirements of GCSE services, for example, GCSE services require a data bearer to be established within 300 ms, but according to eMBMS, an MCE needs to first send signaling to all of eNBs in an MBSFN and the eNBs synchronously transmit MBMS control information via respective air interfaces, the time needed by the process has exceeded the time required by the GCSE services. At present, two methods are proposed to solve the problem. According to one method, eMBMS bearers are established in advance. According to the other method, unicast bearers are established in the network, and data is transmitted to receiving group members via the unicast bearers. Meanwhile, the network starts to establish eMBMS bearers. After the eMBMS bearers are established, data are transmitted to the receiving group members via the eMBMS bearers. Within a time period, data is transmitted via the unicast bearers and the eMBMS bearers simultaneously.
The methods can avoid the delay in bearer establishment, but the following problems are still to be solved.
In current eMBMS systems, an MCE allocates radio resources for eMBMS, and multiple eMBMS channel (MCH) share the eMBMS radio resources. An MBMS channel may be reused by multiple MBMS services. GCSE services characterize in that there is no GCSE data transmission in most of the time in each cyclic time period of a GCSE group and active time in which there is data transmission is very short. In addition, different groups have different active time, and generally do not transmit GCSE service data at the same time. Therefore, data of multiple GCSE services can be transmitted over an air interface in a multiplexing manner to use air interface resources effectively. When the number of users in a group increases or when the number of GCSE user groups increases or when the number of users in a group is unchanged but the amount of to-be-transmitted data increases significantly, there may be a sudden increase in the amount of data and the pre-allocated eMBMS radio resources may become not enough to transmit the increased amount of data. When data exceeds the transmission capacity of the transmission channel, an eNB may discard service data on the last bearer multiplexed on the MCH. A large amount of data loss generates problems in group call services, and UEs and GCSE AS cannot take actions to solve the problems because they do not know the problem.
Another problem is that when group call service data cannot be transmitted properly because resources of some MBMS bearers may be occupied by other services that have higher priority levels or because an eNB malfunctions, UEs and GCSE AS cannot take measures of solve the problem because they do not know the problem. Therefore, a radio access network (RAN) node needs to report the situation to the GCSE AS.
Another problem is that all eNBs within an MBSFN perform the same actions. Therefore, all the eNBs within the MBSFN report the same information, and the repeatedly reported data is redundant for an M2 interface.